CDMA Theory_Nokia Technical Material_Chinese.pdf

诺基亚公司技术资料诺基亚公司技术资料 第第1页页/共共24页页 CDMA Technology Information CDMA 技术信息技术信息 CDMA Technology Information CDMA 技术信息技术信息 Author: 原著： John Danahy Translated by: 翻译：Cui Yuguang Checked by: 校对： Cheng Yan Change History: REV DATE AUTHOR DESC. OF CHANGE 0 11/08/1999 John Danahy Draft 1 08/22/2002 John Danahy CDMA2000 Update 2 Oct 4/2003 Cui Yuguang Start Translate to Chinese 3 Mar 8-11/2004 Cui Yuguang Complete translation 4 Mar 25/2004 Cheng Yan Start checking 5 Apr 05/2004 Cheng Yan Finish checking 6 Apr 06/2004 Cui Yuguang Final Check, Release * NOTE: It is the responsibility of the user of this document to insure it is the most current information available. This document is created and controlled by the Training Department for training purposes only. * 诺基亚公司技术资料诺基亚公司技术资料 第第2页页/共共24页页 CDMA Technology Information CDMA 技术信息技术信息 Contents: 目录目录 SECTION. PAGE 1.0 CDMA Standards History3 2.0 Reverse/Forward Channels3 3.0 Cell Plan.5 3.1 Omni-directional Cell Sites.5 3.2 Sectored Cell Sites.6 4.0 AMPS and CDMA coexistence.6 5.0 Forward Channels6 5.1 Pilot Channels.6 5.1.2 Walsh Codes.8 5.2 Synchronization Channel9 5.3 Paging Channel10 5.4 Traffic Channel12 5.4.1 Forward Vocoder12 5.4.2 Forward Error Protection.12 5.4.3 Interleaving.12 5.4.4 Long Code Generation.13 5.4.5 Closed Loop Power13 5.4.6 Walsh code spreading.13 5.4.7 Short Code spreading14 6.0 Reverse Channels.14 6.1 Access Channel:.14 6.2 Traffic Channel15 6.2.1 Reverse Vocoder.15 6.2.2 CDMA Frames.16 6.2.3 Reverse Traffic Link.19 6.2.4 Open Loop Power.19 6.2.5 Rake Receiver.19 7.0 HandOffs.20 7.1 Soft Handoff20 7.2 Hard Handoff21 8.0 Orthogonal Spreading22 9.0 Differences between IS200 and IS95B.23 诺基亚公司技术资料诺基亚公司技术资料 第第3页页/共共24页页 CDMA Technology Information CDMA 技术信息技术信息 1.0 CDMA Standards History CDMA 标准历史标准历史 May 1995 IS95-A was introduced as the dual mode cellular band interim standard for CDMA. 1995 年 5 月 IS95A 成为 CDMA Cell 频段过渡标准。 June 1996 J-STD-008 was introduced as the CDMA PCS band interim standard. 1996 年 6 月 J-STD-008 被引入成为 PCS 频段过渡标准。 June 1997 IS95-B standard which combine the other two mentioned above with higher voice data rates, also referenced as TSB74 1997 年 IS95-B 标准, 也称为 TSB74 结合了上述两种标准，同时提供了更高的话音编码速率，。 March 2000 CDMA 2000 introduced as the 3G replaces IS95B as new standard. 2000 年 3 月推出的 CDMA 2000 作为 3G 标准，取代了 IS95B 成为新的标准。 2.0 Reverse/Forward Channels 反向反向/前向信道前向信道 Reverse Link is from Mobile to Base Station and the forward link is from base station to mobile. 反向链路是从手机到基站，前向链路是从基站到手机。 All communication in the CDMA system takes place over a single 1.25 MHz frequency block. The maximum capacity for a CDMA cell is 42 users but typically about 20 subscribers share the same channel, simultaneously. There are approximately 42 AMPS channels per CDMA channel. CDMA系统所有的通信都是在一个 1.25MHz 的频段内发生的。一个 CDMA 小区的理论最大容量是 42 个用 户，但是一般情况下，是 20 个用户同时共享同一个信道。在一个 CDMA 信道内大约可以容纳 42 个 AMPS 信道。 诺基亚公司技术资料诺基亚公司技术资料 第第4页页/共共24页页 CDMA Technology Information CDMA 技术信息技术信息 ch. 283 ch. 384 ch. 691 ch. 777 Cellular Band CDMA Channels Cell 频段 CDMA 信道 ch. 25 ch. 50 ch. 75ch. 1125ch. 1150 ch. 1175 BW 1.25 MHz 625 kHz PCS Band CDMA Channels PCS 频段 CDMA信道 Every channel is 50 kHz wide and CDMA channels are in multiples of 25 starting with Ch.25 ending at Ch.1175. 625 kHz BW 1.25 MHz 诺基亚公司技术资料诺基亚公司技术资料 第第5页页/共共24页页 CDMA Technology Information CDMA 技术信息技术信息 3.0 Cell Plan: 小区规划小区规划 In the CDMA network adjacent cells can and do use the same frequencies. Shown in the diagram below. The reason that this is possible is because CDMA is designed to decode signals correctly in the presence of high levels of interference. By reusing the same CDMA channel in each and every sector and cell in the system there is a lot less frequency planning compared to the other protocols. 在 CDMA网络中，相邻的小区可以同频复用，如下图所示。这是因为 CDMA可以在较强干扰情况下正确解 调信号而使频率复用成为可能。每个蜂窝小区和扇区使用同一个 CDMA信道，使得 CDMA的频谱规划与其 它协议相比相对简单。 1 2 3 4 5 6 7 7 6 3 7 1 6 1 2 4 2 3 4 5 5 6 1 2 3 4 5 7 Analog base station A passes this request to the MSC (Mobile Switching Center). The MSC passes the request to station B to see if a traffic channel is available for the soft hand-off request. CDMA软切换的发起： 下面的情形描述了如何发起一次软切换。一个手机正在使用来自信号A的连接同时开始接收来自B 的信号。当信号B超过由B基站定义的“加入阈值”水平时，一个导频强度信号从手机发送到基站 A。导频强度信息通过业务信道发送，使用暗淡-突发或者空白-突发信令模式。导频强度信息发起了 软切换的过程。当基站A接收到导频强度信息后，就向MSC(移动交换中心)发送请求。MSC将此 请求发送到基站B，看看B基站是否有空闲的业务信到来接受软切换的请求。 诺基亚公司技术资料诺基亚公司技术资料 第第21页页/共共24页页 CDMA Technology Information CDMA 技术信息技术信息 CDMA Soft Hand-off If a channel is available, cell site B sends the Walsh Code that will be assigned for the soft hand-off to the MSC. At this point base station A orders the soft hand-off by sending a hand-off direction message to the mobile using the traffic channel. When the hand-off message is acknowledged, the MSC sends the land link to base station B who then begins to send information on the assigned Walsh code traffic channel to the mobile. The mobile then receives both signals from the two cell sites, each operating on different PN offsets and Walsh coded traffic channels. The two signals are then combined by using the two pilot signals as coherent phase references. In a two way soft hand-off, two of the mobiles rakes are used: one for each received base station At the same time both base stations are independently receiving the mobiles signal. The demodulated signal is sent to the MSC where the two signals are compared on a frame-by-frame bases. The MSC selects the better of the two signals and sends that signal to the CODEC where it is passed to the public telephone network. CDMA软切换的过程： 如果有空闲信道，基站B就把需要用来赋予软切换的Walsh码发送到MSC。同时基站A通过业务 信道发出一个切换方向信息给手机以发起软切换。当切换信息得到确认后，MSC就发送陆地链路给 基站B，基站B开始在指定的Walsh码的业务信道上发送信息给手机。此时手机会同时接收到两个 基站的信号，彼此运行在不同的PN偏移和Walsh码业务信道上。通过使用两个导频信号作为相干 参考相位将两个信号合并起来。在双向软切换过程中，要使用手机的两个Rake接收机：分别用来 接收来自各自的基站信号。同时两个基站都在独立地接来自收手机的信号。经解调后的信号送到 MSC，在这里两个信号进行以帧对帧为基础的比较。MSC将选择其中一个较好的信号，将它发送 到CODEC（编解码器），从这里进入公共电话网络。 CDMA Hand-off Completion When the signal from station A degrades and goes below “Drop Threshold” the mobile sends another pilot strength message to base station B indicating that base station As link should be terminated. At this point the mobile is being power controlled by base station B. The mobiles' request is passed by the MSC to cell site A to terminate transmission and reception of the mobiles signal. The mobile is now exclusively terminated with base station B. CDMA软切换的结束： 当基站A的信号衰落并下降到低于“取出阈值”的时候，手机就发出另一个导频强度信息给基站 B，指示基站A的链路将要终止。此时手机的功率控制将完全由基站B进行。手机的请求通过MSC 发送给基站A，以终止基站A同手机之间的发送和接收。此时手机已经完全切换到基站B。 If the hand-offs are between sectors on a base station the same routine applies. It makes no difference to the mobile whether the hand-off is between sectors or cell sites. 如果切换是在同一个基站的不同扇区之间，也适用同样的规程。对于手机来说，在扇区之间或在基 站之间切换是没有什么区别的。 7.2 Hard Handoff 硬切换硬切换 Most CDMA handoffs are soft, that is make before break however some types of handoffs are break before make. An example of a hard handoff would be from CDMA to analog, the CDMA link would have to be broken before the analog link is made. A mobile can not run in CDMA and analog mode at the same time. Another type of hard handoff would be a change of CDMA channels. At present 800 Mhz cellular providers have two CDMA channels per provider. 大多数的CDMA切换都是软切换，即先连接后切断；然而有一些切换却是先切断后连接，这就是 硬切换。硬切换的一个例子是从CDMA系统切换到模拟系统，此时CDMA的链路必须先切断然后 模拟的链路才能建立起来。手机不能够同时工作在CDMA和模拟模式下。另外一种硬切换是切换 到不同的CDMA物理信道。由于目前的800兆赫蜂窝系统给每个运营商分配了两个CDMA物理信 道，这种切换理论上是可以发生的。